Pressure measurement cells of the field of the invention are disclosed, for example, in published international application, WO 2011/006741 A1, European patent, EP 0 373 536 A2 and published international application, WO 2011/003730 A1 as well as in documents mentioned therein. An overview of electrical transducer principles and a description of the deformation of measuring membranes and the resulting mechanical stresses is explained by Pfeifer and Werthschützky in “Drucksensoren (Pressure Sensors)”, Berlin, 1989. It should be noted that the nomenclature in the mentioned publications is not uniform. The measuring membranes according to WO 2011/006741 A1, WO2011/003730 A1, respectively the present invention, are plates, especially circular plates in the sense of Pfeifer and Werthschuetzky, respectively EP 0 373 536 A2.
A problem with measuring membranes is their limited overload resistance. On the one hand, the measuring membranes should be sufficiently thin, in order in the desired measuring range to be deflectable with a usable amplitude, and, on the other hand, they should withstand an overload pressure, which can be a multiple of the measuring range.
In order, nevertheless, to be able to apply sufficiently sensitive measuring membranes, approaches for overload protection of the measuring membrane are known that involve support in the case of overload, for example, support by membrane beds. In such case, the measuring membrane should in the case of exceeding a limit value for the positive pressure be at least sufficiently supported on the membrane bed that the bursting stress of the measuring membrane is not reached even in the case of an additional pressure rise. For such purpose, especially aspherical membrane beds are suitable, which approximate the bend line of the measuring membrane at the limit value for the positive pressure. Corresponding membrane beds are disclosed in U.S. Pat. No. 4,458,537, German patent, DE 10 2009 046 229 A1, U.S. Pat. No. 7,360,431 B2, German patent, DE 10 2010 028 773 A1, Japanese patent, JP10078366A and U.S. Pat. No. 5,381,299. European patent, EP 0 373 536 A2 discloses a pressure sensor, which provides a support ring for annular support of the measuring membrane in the case of an overload.
German patent, DE 10 2010 028 504 A1 discloses a pressure sensor with a platform having a planar surface and a measuring membrane having in the resting position a concave surface, which faces the platform. When the measuring membrane is deflected by pressure loading from the side facing away from the platform toward the platform, the concave surface of the resting position assumes exactly at the degree of deflection a planar shape, in the case of which the measuring membrane contacts the platform. In this way, a full surface support of the measuring membrane is achieved, and a further rise of mechanical stresses in the measuring membrane is reliably prevented. A similar approach is described in European patent, EP 0439 494 B1. The measuring membrane additionally includes, compared with the concave region, an thinner, ring-shaped, edge region, which surrounds the concave region. Therewith, the membrane is more easily deflectable, and the maximum stresses in the edge region in the case of a given deflection of the measuring membrane are smaller than would be the case with an uninterrupted continuing of the concave contour up to the outer edge of the measuring membrane.